The present invention relates to a digital image coding method, a digital image coding apparatus, a digital image decoding method, a digital image decoding apparatus, a data structure for image transmission, and a data recording medium in which a program for implementing these methods or apparatuses in software is stored and, more particularly to a method in which an image is divided into plural regions and coded with improved efficiency.
In recent years, we have been in the age of xe2x80x9cmultimediaxe2x80x9d which handles audio, video, and other data integratively. The multimedia is used to transmit information of conventional information media, namely, newspapers, magazines, televisions, radios, telephones, and so forth, to users. In general, in the multimedia, graphics, sound, images, and so forth, as well as characters, are related to each other simultaneously. It is essential that information of the conventional information media be in a digital format so that it is intended for the multimedia.
Information of each information medium is given in terms of amount of digital information. For example, characters require information of 1 to 2 bytes per character, while sounds require information of 64 kbits (telephone quality) per second, and further, moving pictures require information of 100 Mbits or more (current television receiving quality) per second. So, with respect to the information medium of image information, its enormous amount of information cannot be handled in a digital format. For example, although visual telephones have already been put to practical use by means of an ISDN (Integrated Services Digital Network) which accommodates a transmission rate ranging from 64 kbps to 1.5 Mbps, video of TV or camera cannot be directly sent over the ISDN.
Accordingly, there is a need for a compression technique for information. In case of visual telephones, a moving picture compression technique according to H 261 standard which is internationally standardized-by an ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) is employed. Also, according to an information compression technique conforming to MPEG (Moving Picture Experts Group) 1 standard, audio and video information can be recorded in a normal CD (compact disc) for music.
The MPEG is an international standard for data compression of a moving picture. According to the MPEG1, moving picture data is compressed into 1.5 Mbps data, that is, TV signal information is compressed to about 1/100 information. Since a transmission rate of the MPEG1 is restricted to about 1.5 Mbps, according to MPEG2 standardized to meet demands of a higher image quality, the moving picture data is compressed into 2 to 15 Mbps data.
In status quo, MPEG4 is being standardized by a group (ISO/IEC JTC1/SC29/WG11) which has standardized MPEG1 and MPEG2. According to the MPEG4, coding image information for each object on a display screen and required signal processing can be performed, and new capabilities needed for multimedia can be provided.
According to MPEG4, for higher efficiency in coding, a display image is divided into plural regions depending on contents of a display image, and then an image signal of each region is compressively coded. The divided region is an object region for each object of a display image. Such coding method is disclosed in Japanese Published Patent Application No. Hei 2-279080 or Japanese Published Patent Application No. Hei 7-38896.
In the compressive coding described above, it is necessary to compressively code shape information of each region (region shape information) as well as a brightness signal or a color difference signal of each region. For example, chain coding is often used to code the region shape information.
In the case where the image is divided into plural regions, at a boundary between adjacent regions, these regions have shapes corresponding to negative and positive patterns in a photograph, and it is not therefore undesirable to code image signals of respective regions separately when considering efficiency in coding. In other words, if a boundary shape ot one ot the adjacent regions is known, then a boundary shape of the other region is known, so that a shape signal of one of the adjacent regions is coded, while a shape signal of the other region is coded after eliminating data indicating the boundary shape, thereby reducing amount of shape signals to be coded.
In another case where image signals of plural regions into which an image is divided and image signals of plural images to-be-composited are coded and transmitted/recorded, images of respective regions, or composition information for overlapping the respective images to-be-composited, are transmitted together with coded data of respective images. The composition information contains information indicative of relationship of order (before and behind) among the respective images to be overlapped. In decoding, image signals of respective images are coded, and then decoded image data is composited in the order of the composition information.
However, there have been several drawbacks with such prior art image coding, which are described below.
One problem is that a shape of a transformed region cannot be regenerated unless coded data of all regions of a frame is decoded and regenerated, since adjacent regions required for restoring the transformed shape are not recognized in a decoding end.
Another problem is that there is a possibility of decoding data which is not required for decoding and regenerating an image of a required region when decoding the required region or specific images to-be-composited, since the composition information only indicates the order relationship.
It is an object of the present invention to provide a digital image coding method and a digital image coding apparatus in which adjacent regions required for restoring the transformed shape in its coding process can be obtained from adjacent region lists, thereby sequentially decoding and regenerating coded data of transformed regions without the need for decoding and regenerating coded data of all regions of a frame, in a decoding end.
It is another object of the present invention to provide a digital image decoding method and a digital image decoding apparatus in which appropriate decoding can be performed to a coded image Signal which have been coded by the digital image coding method and the digital image coding apparatus.
It is still another object of the present invention to provide a data recording medium which stores a digital image coding program and a digital image decoding program for implementing the image coding method and the image decoding method in general purpose apparatuses such as personal computers or work stations.
It is a further object of the present invention to provide a data structure for image transmission in which adjacent regions required for restoring the transformed shape in its coding process can be obtained from adjacent region lists, thereby sequentially decoding and regenerating coded data of transformed regions without the need for decoding and regenerating coded data of all regions of a frame, in a decoding end.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the spirit and the scope of the invention will be apparent to those skill in the art from the detailed description.
According to one aspect of the present invention, a digital image coding method comprises the steps of: dividing an image into plural regions each having an arbitrary shape, subjecting an image signal of a required region of the plural regions to transformation so that an arbitrary shape of the required region of a boundary between the required region and a region adjacent thereto is transformed, and compressively coding the image signal of the required region and compressively coding image signals of regions except the required region without subjecting them to transformation; generating identifiers for identifying respective regions; generating list information which describes an identifier of at least one region adjacent to the required region, which is required for restoring the transformed shape to the shape before transformation; and outputting compressively coded data in which image signals of respective regions have been compressively coded, the identifiers of respective regions, and the list information as a coded image signal. Therefore, adjacent regions required for restoring the transformed shape in its coding process can be obtained from adjacent region lists, thereby sequentially decoding and regenerating coded data of transformed regions without the need for decoding and regenerating coded data of all regions of a frame, in a decoding end.
According to another aspect of the present invention, a digital image decoding method for decoding and regenerating a coded image signal which has been compressively coded by a digital image coding method of the first aspect, comprises: a decoding step for decoding compressively coded data included in the coded image signal to regenerate image signals of respective regions, wherein a regenerated image signal of the required region is restored by a prescribed process according to list information and shape information of at least one required adjacent region which are included in the coded image signal so that a shape of the required region is restored to its arbitrary shape before transformation. Therefore, the present invention provides an image decoding method and an image decoding apparatus in which the coded image signal has been coded by the image coding method and the image coding apparatus are appropriately decoded.
In addition, the list information is added to each compressively coded data. Thereby, when regenerating a required region or image, compressively coded data required for regenerating a required region can be decoded by referring to the list, which reduces amount of data to-be-decoded, resulting in high-speed decoding.
Further, the list information is added to each compressively coded data or for each compressively coded data of a prescribed number to regenerate a required region. Thereby, it is not necessary to obtain composition information which describes overlapping relationship among respective regions required for regenerating all regions.
According to still another object of the present invention, in a data recording medium, a program for making a computer perform the digital image coding and digital image decoding is stored, and by loading the program into the computer, efficiency in coding and decoding is improved.
According to a further object of the present invention, a data structure for image transmission for transmitting a coded image signal in which a digital image signal has been coded, comprises: coded data obtained by subjecting an image signal of a required region of plural regions each having an arbitrary shape to transformation so that an arbitrary shape of the required region of a boundary between the required region and a region adjacent thereto, and compressively coding the image signal of the required region and by compressively coding an image signal of a region other than the required region without it is transformed; identifiers for identifying respective region; and list information which describes identifiers of adjacent regions required for restoring the transformed shape of the required region to its arbitrary shape before transformation. Therefore, adjacent regions required for restoring the shape which has been transformed in its coding process can be obtained from adjacent region lists, thereby sequentially decoding and regenerating coded data of transformed regions without the need for decoding and regenerating coded data of all regions of a frame, in a decoding end.